Slime city

By Andy Coghlan

THROUGH the murky gloom, you can just make them out – shadowy towers shaped like mushrooms. Circulating through and around them, apparently suspended in mid-air, there are ducts and channels of swishing liquid. Just for a moment, the murk clears. In the distance, you see skyscrapers of ghostly spheres piled one on top of the other.

The set of a futuristic movie on some distant planet? Not quite. This is slime city, a sprawling metropolis very much of this world. Inside, shielded from harm and replete with every creature comfort, live beings whose cosmopolitan lifestyle is only now coming to light.

Amazing cityscapes like this have existed on Earth for billions of years, built and populated by plain, humble bacteria such as Escherichia coli and salmonella. More properly known as biofilms or mucilages, slime cities thrive wherever there is water – in the kitchen, on contact lenses, in the gut linings of animals. When the urban sprawl is extensive, biofilms can be seen with the naked eye, coating the inside of water pipes or dangling slippery and green from plumbing.

Yet only in the past few years have scientists learnt how to observe the inner structures of biofilms using powerful microscopy techniques. What they are now discovering about those ghostly cityscapes is sending shock waves through microbiology.

Toxic food

For decades, microbiologists have based virtually all their ideas about bacteria – how fast they can grow, how they react to antibiotics, what they can eat, and so on – on the behaviour of colonies grown from single species on laboratory plates. But research now shows that in nature, bacteria …

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